A light emitting diode (LED) is rapidly expanding its market for a backlight of a liquid crystal display (LCD) and for general lighting in addition to lighting in automotive applications such as headlight because of a low power consumption, a long life time and design against the background of significant improvement in luminance efficiency.
An emission color of an LED is limited since an emission spectrum of the LED depends on a semiconductor material for forming an LED chip. Therefore, in order to obtain LCD backlight or white light for general lighting by using an LED, it is necessary that a phosphor suitable for an LED chip is arranged on the LED chip to convert an emission wavelength. Specifically, a method of disposing a yellow phosphor on an LED chip that emits blue light, a method of disposing a red phosphor and a green phosphor on an LED chip that emits blue light, a method of disposing a red phosphor, a green phosphor and a blue phosphor on an LED chip that emits ultraviolet light, and the like are proposed. Among these methods, the method of disposing a yellow phosphor on an LED chip that emits blue light, and the method of disposing a red phosphor and a green phosphor on an LED chip that emits blue light are currently most widely employed from the viewpoints of luminance efficiency and cost of an LED chip.
Patent Documents 1 to 3 propose a method of bonding a sheet containing a phosphor (hereinafter, referred to as a phosphor sheet) to an LED chip as a specific method of disposing a phosphor on an LED chip. This method is superior in that a constant amount of a phosphor can be more easily arranged on an LED chip than a method of dispensing a liquid resin, in which a phosphor heretofore put to practical use is dispersed, on an LED chip and curing the resin, and color and luminance of the resulting white LED can be uniform.